This invention relates to a closed cell phenolic foam and to a process for preparing such foams from resins.
Phenolic foams are widely used in building applications in view of their thermal insulation and fire resisant properties. Such phenolic foams are generally prepared by mixing a phenol formaldehyde resin with a blowing agent, a cell stabiliser and a hardener.
EP-A-0170357 describes one such process for preparing a phenolic foam using Freon as a blowing agent, aqueous sulphuric acid as a hardener, and a cell stabiliser derived by oxylating castor oil with ethylene oxide or mixtures thereof with proplylene oxide. Freon is a particular chlorofluorocarbon (CFC).
EP-A-0439283 describes the use of a complex blend of materials as an alternative blowing agent to a CFC The blend comprises: at least one perfluoroalkane (PFA) (especially perfluoropentane, perfluorohexane or perfluoroheptane); and at least one component selected from a hydrogenated chlorofluorocarbon (HFC) and a specific alkane or cydoane.
EP-A0579321 descries a phenolic foam including pezffuro-N-methyl morpholine.
WO-A-9811715 describes the manufacture of resol foams using perfluorinated ethers as part of the blowing agent blend.
There is a need for an improved phenolic foam which is easily processed, environmentally friendly and has good thermal conductivity properties.
According to the invention there is provided a closed cell phenolic foam formed from a phenolic resin, a blowing agent, a catalyst and at least one hydrofluroether or an azeotrope formulation thereof in an amount of less than 2.5% by weight relative to the resin to form a phenolic foam having a closed cell content of greater than 90% and a stable thermal conductivity.
Most preferably the hydrofluroether is present in an amount of from 0.5% to 1.5% by weight relative to the resin.
In a preferred embodiment of the invention the hydrofluoroether is of the general formula CaFbOCH3 or CaFbOC2H5 wherein:
b=2a+1
Preferably the hydrofluoroether is C4F9OCH3 (1-methoxy-nonafluorobutane).
Ideally the hydrofluoroether is in an azeotrope formulation, especially with trans-1,2 dicloroethylene.
In a particularly preferred embodiment the azeotrope formulation is a 50/50 formulation of 1-methoxy-nonaffuorobutane with trans 1,2, dichloroethylene.
The azeotrope formulation may be formed by a reaction of two or more components, at least one component being present in the phenolic resin.
The blowing agent may include a hydrogenated chlorofluorocabon (HCFC). Ideally, the HCFC is HCFC 14Ib (CCl2Fxe2x80x94CH3).
Alternatively the blowing agent may include a hydrogenated fluorocarbon (HFC).
The foam may include an alkane or cycloalkane.
In a particularly preferred aspect the invention provides a closed cell phenolic foam formed from a phenolic resin, a blowing agent, a catalyst and less than 2.5% by weight relative to the resin of 1-methoxy-nonaflurobutane or an azeotrope formulation-thereof with trans-1,2-dichloroethylene.
In a preferred aspect the invention provides a closed cell phenolic foam from a phenolic resin, HCFC 141 b (CCl2Fxe2x80x94CH3) a catalyst and less than 2.5% by weight relative to the resin of 1-methoxy-nonaflurobutane or an azeotrope formulation thereof with trans-1, 2-dichloroethylene.
In an especially preferred aspect the invention provides a dosed cell phenolic foam formed from a phenolic resin, HCFC 1416 (CCl2Fxe2x80x94CH3), a catalyst and less than 2.5% by weight relative to the resin of an azeotrope of 1-mehoxy nonaflurobutane wit trans-1,2-dichloroethylene.
Preferably the catalyst is a strong mineral acid such as sulphuric acid counting at least 20% water, preferably at least 40% water.
The invention fire provides a blend for forming a closed cell phenolic foam of the invention, the blend comprising a blowing agent, a catalyst and less than 2.5% by weight relative to a phenolic resin of at least one hydrofluroether or an azeotrope formulation thereof.
The invention will be more clearly understood from the following description thereof given by way of example.
The invention is based on the surprising finding that closed cell phenolic foams can be produced by using relatively small quantities of at least one hydrofluoroether (HFE). It is believed that the HE acts as a surfactant.
Ethers are usually strong solvents which can have an adverse cell opening effect on foam and would therefore not normally be considered as suitable components for closed cell foams. We have however, surprisingly found that hydrofluoretheres can be effectively used as surfactants in foam formulations.
In addition to this unexpected use of such ethers, there is the further major advantage that these solvents have much less environmental impact than conventional solvents used in foam manufacture. Such solvents have a very low global warming potential when compared with conventional solvents used in such foam formulations.
Most importantly and unexpectedly we have found that not only is a highly closed cell foam produced using a hydrofluroether with a low global warning potential but also the foam produced has an extremely favourable stable thermal conductivity profile.
The dosed cell value may be measured by the method described in B.S. 4370/ASTM D2856. The foam of the invention has a closed cell content of greater than 90% when measured by this method.
The K value is measured as described in method 7A of B.S. 4370 part 2 with reference to B.S.3927. ASTM C177 is equivalent. The preferred foam of the invention has a K value at 30 days or longer of less than about 0.018 W/Mxc2x0C. Even more surprisingly the thermal conductivity remains stable when tested at high temperatures of about 70xc2x0 C. over prolonged periods.